if every slave owner and klansman were put to death for their heinous crimes

Their property would have passed to their heirs.

If your only available tool was killing people, then maybe you could have followed it up by killing their children?

But then you have to contend with the fact that your movement (and the people you have handed weapons to) are now a very specific subset of communists -- "communists who are okay with killing children." You can't build a country off of that!

If on the other hand you have some way of stopping slaveowners' heirs from receiving their fortunes without killing those heirs, then you clearly have some tool that can void the property of the slaveowners themselves without killing them.

And once again, if you choose to kill the slaveowners despite possessing such a tool, then you wind up building your movement off of, "people who are fine with killing when it's no longer necessary." After that, it's no surprise when that movement starts blowing up a bunch of members of Hungarian soviets -- the very people the movement claims to protect -- with tanks.

Yeah, I think their plantations should have been taken from them. Yeah, I think Klansmen should have been stripped of everything they owned.

But once you're powerful enough to do that, you're also powerful enough to do that without killing them.

If they throw their bodies in front of the Orphan Crushing Machine, don't let that stop your bullets. But if they step aside, you have a choice: align yourself with people who kill when they don't need to, or align yourself with people who avoid killing whenever possible.

One of those is better than the other.